1. Field of the Invention
The present invention relates generally to fuel cell systems and, more particularly, to a new and improved fuel cell system having a combined injector/ejector system.
2. Discussion of the Related Art
A fuel cell is a device that generates electricity by a chemical reaction. Every fuel cell has two electrodes, one positive and one negative, called, respectively, the cathode and the anode. The reactions that produce electricity take place at the electrodes. Every fuel cell also has an electrolyte, which carries electrically charged particles from one electrode to the other, and a catalyst, which speeds the reactions at the electrodes. Hydrogen is the basic fuel, but fuel cells also require oxygen. One advantage of fuel cells is that they generate electricity with very little pollution, i.e., much of the hydrogen and oxygen used in generating the electricity ultimately combine to form a harmless byproduct, namely water.
With respect to fuel cell operation, in general terms, hydrogen atoms enter a fuel cell at the anode where a chemical reaction strips them of their electrons. The hydrogen atoms are now “ionized,” and carry a positive electrical charge. The negatively charged electrons provide the current through wires to do work. If alternating current (AC) is needed, the DC output of the fuel cell must be routed through a conversion device called an inverter.
Oxygen enters the fuel cell at the cathode and, in some cell types, it combines with electrons returning from the electrical circuit and hydrogen ions that have traveled through the electrolyte from the anode. In other cell types, the oxygen picks up electrons and then travels through the electrolyte to the anode, where it combines with hydrogen ions. The electrolyte permits only the appropriate ions to pass between the anode and cathode. If free electrons or other substances could travel through the electrolyte, they would disrupt the chemical reaction.
Whether they combine at the anode or the cathode, together hydrogen and oxygen form water, which drains from the cell. As long as a fuel cell is supplied with hydrogen and oxygen, it will generate electricity.
In a conventional fuel cell system, a mixture of gases, such as H2, H2O and N2, are transported from the anode outlet back to the anode inlet of the fuel cell system (e.g., a “stack” of individual fuel cells). Generally speaking, an injector is typically associated with the inlet side and an ejector is typically associated with the outlet side.
In one method, injectors and ejectors are constructed and deployed for fuel injection and anode gas re-circulation as separate and spaced components, the two being in fluid communication by virtue of a conduit/piping system. Re-circulation motive force is taken from fuel cell tank pressure energy, and is regulated to track and motivate anode re-circulation load. Anode re-circulation load comes from nitrogen (carried over from the cathode side) and from water (reaction product). Nitrogen must be removed from the loop by venting. Since this method tracks hydrogen pressure solely with nitrogen loading, hydrogen venting increases with nitrogen venting. Reduced fuel utilization is therefore a major disadvantage of this ejector re-circulation method where nitrogen is present in the anode gas.
In another method that is an alternative to the ejector method discussed above, a pumping device can be employed to deliver the respective gases back into the inlet of the fuel cell system. This method has the utilization advantage that hydrogen pressure tracks only the engine power fuel requirement. However, pumping power increases with re-circulation load, thus detracting from the overall energy efficiency of the fuel cell system.
Therefore, a need exists for a new and improved fuel cell anode gas re-circulation system, wherein the injector and the ejector are configured in such a manner so as to improve both the overall operation and energy efficiency of the fuel cell system.